Enhanced Levels of Pan and Ozone in the Nighttime Boundary Layer over Berlin, Germany

In July and August 1998 the comprehensive field campaign BERLIOZ(“BERLIN OZON”) took place in the Greater Berlin Area, Germany. This project focused on photochemical processes in the urban plume and covered a wide range of simultaneous measurements of meteorological parameters and air chemical compounds at various ground-based sites as well as aboard airborne facilities (e.g. H2 gas balloon). As an extraordinary site located on the borderline of the urbanized area of Berlin the Frohnau Tower formed part of the monitoring network. Apart from a measurement site at its bottom, also one continously working measurement site was located on top of the Frohnau Tower at an altitude of 324 m a.g.l.. This allowed monitoring free boundary layer conditions on a routine basis. This paper presents an event that occurred during nighttime from August 6-7, 1998, when unusually enhanced values of ozone and PAN were observed at the top of Frohnau Tower. The ozone values were among the maximum values, in case of PAN they actually represented the highest ones registered on all sites during the entire BERLIOZ campaign. In this night polluted air masses passed the Berlin area. However, only the free boundary layer was affected, whereas these air masses hardly reached the surface layers. This paper elucidates meteorological and air chemistry conditions and discusses transport processes.